The present invention relates to a method for preparing stereo images by taking images of an object at least from two directions and for preparing stereo images from a plurality of images thus taken. The present invention also relates to a system for preparing 3-demensional data based on a stereo image by associating the stereo image with measured data.
A stereo image is an image to represent an object stereoscopically, and the stereo image is an image acquired through image pickup of the same object by changing image pickup directions. By associating points on respective images with each other, it is possible to obtain 3-dimensional data of points, which constitute the image.
For the purpose of obtaining 3-dimensional data from a stereo image, it is necessary to perform matching of two images (stereo-matching), and conditions to enable to perform stereo matching (external orientation elements) are required. As the external orientation elements, 3-dimensional data, image pickup directions, tiltings, magnifications, etc. of two image pickup points (camera positions) are respectively required.
In order to perform stereo matching of two images, it is necessary to have relative rotation of left and right cameras with respect to a base line vector between the left and right cameras, i.e. relative orientation elements. The relative orientation elements are calculated based on the external orientation elements.
In the past, when a stereo image is to be prepared, images of an object are taken by a camera from two known points respectively, and external orientation elements necessary for calculating relative orientation elements are obtained. For this reason, it is necessary to set reference points on the object, to separately measure the reference points by a total station or the like, and to find positions and tiltings of the cameras based on 3-demensional position information of the reference points.
In this respect, it is necessary to perform photogrammetry to obtain a stereo image, to set reference points (pass points) in the image after photogrammetry, and to perform measurement on the reference points by a surveying instrument such as a total station from two known points where images have been taken respectively. Moreover, six or more pass points are required, for instance, and this leads to complicated measuring operation.